package UdpServerAndClient;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    public void start() throws IOException {
        System.out.println("服务器启动！");
        while(true){
            //1.读取请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);
            //为了方便在 Java 代码中处理（尤其是后面的打印）可以把上述数据报中的二进制数据，拿出来，构造成String
            String request = new String(requestPacket.getData(),0,requestPacket.getLength());
            //2.根据请求计算响应
            String response = process(request);
            //把响应写回客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),0,response.getBytes().length
                                            ,requestPacket.getSocketAddress());
            //发送
            socket.send(responsePacket);

            System.out.printf("[%s:%d] req=%s , resp=%s\n",responsePacket.getAddress(),requestPacket.getPort(),
                            request,response);
        }
    }

    //当前写的是“回显服务器”
    public String process(String request){
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}
